1. Field of Invention
The present invention relates generally to a method of dry etching semiconductor wafers. More specifically, the invention relates to a method of etching high K dielectric materials using a gas mixture comprising a halogen gas and a reducing gas.
2. Description of the Background Art
Field effect transistors that are used in forming integrated circuit generally utilize a polysilicon gate electrodes deposited upon a gate dielectric that separates the electrode from the channel between source and drain regions. In prior art transistor structures, the gate dielectric is typically fabricated of silicon dioxide (SiO2). However, as integrated circuit transistors have become smaller (on the order of 100 nanometers in width), the thickness of the dielectric material in the gate structure has become thinner than 10 Angstroms. With such a thin dielectric, electrons can propagate from the polysilicon gate electrode into the transistor channel causing the transistor to operate improperly or become defective.
This leakage of electrons from the gate electrode through the gate oxide has led researchers to investigate the use of more stable high K dielectric materials. One very stable dielectric material having a high dielectric constant is hafnium-oxide (HfO2). However, hafnium-oxide is such a stable dielectric material that it is very difficult to etch using conventional oxide etchants to form into gate structures without damaging other layers of material residing on the wafer. As such, hafnium-oxide has found limited use in semiconductor devices.
Therefore, there is a need in the art for a high K material etching process having very high selectivity to silicon oxide, polysilicon and silicon.
The disadvantages associated with the prior art are overcome by the present invention for etching materials with high dielectric constants (high K materials have a dielectric constant greater than 4.0) such as HfO2, ZrO2, Al2O3, BST, PZK, ZrSiO2, HFSiO2, TaO2, and the like using a gas mixture comprising a halogen gas and reducing gas. In one embodiment of the invention, an etch gas (or mixture) comprising chlorine (Cl2) and carbon monoxide (CO) is used for etching hafnium-oxide films. In one example, the gas flow rates are in the range 20-300 sccm Cl2 and about 2-200 sccm CO (i.e., a CL2/CO flow ratio (0.1-1):(1-0.1)), with a total chamber pressure in the range of 2-100 mTorr.
A decoupled plasma source etch reactor is illustratively used to practice one embodiment of the present invention. In general, the reactor uses an inductive source power of about 200-2500 W for plasma generation, and applies a cathode bias power of about 5-100 W to a wafer support pedestal. The reactor maintains the pedestal within a temperature range of about 100 to 500 degrees Celsius. The invention can be practiced, for example, by supplying to the reactor a combination of about 40 sccm of chlorine gas and about 40 sccm of carbon monoxide gas, while maintaining a total chamber pressure of about 4 mTorr. The gas mixture is supplied to the reaction chamber wherein a plasma is formed and a hafnium-oxide layer is etched.